Planar speaker

ABSTRACT

A sound generating transducer or speaker including a vibratable diaphragm on a frame and in spaced and confronting relation with a polarity defining backing, preferably magnetic in nature, conductive means on the diaphragm to receive an audio frequency electric signal to cause attraction and repulsion between the diaphragm and the backing, the diaphragm being divided into definite vibratable areas by divider strips bearing against the diaphragm such that each diaphragm area has a fundamental resonant frequency different than other adjacent areas. The ends of the divider strips are spaced from one edge of the diaphragm to define a long strip-like edge portion of the diaphragm which transcends the several vibratable areas of the diaphragm. The conductive means are separate bass and mid-range audio frequency signal conductors and high range audio frequency signal conductors on the diaphragm and separated in distinct zones, the high range audio frequency signal conductors located in a zone extending along the strip-like edge portion and defining a long, narrow tweeter transcending the several vibratable areas and through the edge areas of the several vibratable areas or woofers which are excited by the signal current in the bass and mid-range audio frequency signal conductors. The mid-range audio frequency signals may be separately applied along another edge portion or zone of the diaphragm in a separate conductor on the diaphragm.

United States Patent l l Winey l l PLANAR SPEAKER James M. Wine), WhiteBear Lake. Minn.

[75} inventor:

[73] Assignee: Magnepan. Incorporated. White Bear Lake. Minn.

[22] Filed: Jan. 11. I974 {Ill Appl. No.1 434,214

Primary E.\airliner-William C. Cooper Ass/slam [italm'aerGeorge G.Stellar Attorney Agent. or FirmH. Dale Palmatier; James R. Haller [57]ABSTRACT A sound generating transducer or speaker including a \ihratahlediaphragm on a frame and in spaced and ll Nov. 11. 1975 confrontingrelation \\ith a polarit defining hacking. preferabl} magnetic innature. conductive means on the diaphragm to recei\e an audio frequencelectric signal to cause attraction and repulsion between the diaphragmand the hacking. the diaphragm being di- \ided into delinite \ihratahleareas h divider strips hearing against the diaphragm such that each diaphragm area has a fundamental resonant frequency different than otheradjacent areas. The ends of the divider strips are spaced from one edgeof the diaphragm to define a long strip-like edge portion of thediaphragm which transcends the several \ihratable areas of thediaphragm. The conductive means are separate bass and mid-range audiofrequenc signal conductors and high range audio frequenc signalconductors on the diaphragm and separated in distinct zones. the highrange audio frequenc signal conductors located in a ZUIIC extendingalong the strip-like edge portion and defining a long. narrow tweetertranscending the se\eral \ihratahle areas and through the edge areas ofthe several \ihratahle areas or woofers which are e\cited h the signalcurrent in the bass and mid-range audio frequenc) signal conductorsv Themid-range audio irequenet signals ma he separatel) applied along anotheredge portion or zone of the diaphragm in a separate conductor on thediaphragm.

[9 Claims. l5 Drawing Figures US. Patent Nov. 11, 1975 Sheet 1 0123,919,499

III/IIIJ] PLANAR SPEAKER BACKGROUND OF THE INVENTION Loudspeakersemploying vibrating planar diaphragms to produce the sounds have beenpreviously known, and certain advantages have been obtained as comparedto cone speakers with wound signal coils As described in my US Pat. No.3,674,946, diaphragm areas having various resonant frequencies. andbeing stretched beyond a mere taut condition. contribute materially tohigh level of output from such speakers.

SUMMARY OF THE INVENTION It has been discovered that in a diaphragm typetransducer or speaker, it is very desirable that high audio frequencysounds be produced and emanate from a narrow and long strip-like zone orarea of the diaphragm. If such a strip-like tweeter zone is oriented inupright position, the high audio frequency sounds will emanatehorizontally in substantially all directions. that is to say. willemanate directly out in front of the diaphragm and the strip-like zoneand also to the left and to the right at all various angles. Similarly,because the generally rigid backing for the transducer is acousti callytransparent, such high audio frequency sounds will also emanatehorizontally to the rear of the dia phragm in substantially alldirections.

The actual magnitude of vibration or excursion of diaphragm areasproducing such high audio frequency sounds is extremely small. amountingto only a few thousandths of an inch. Because of this incrementaldiaphragm excursion in the tweeter zones, the magnet or source ofmagnetic field may be located very close to the diaphragm. It has beenfound that the diaphragm and the conductors thereon in the strip-liketweeter zone should be quite close to the magnet so the magnetic fieldwill have maximum intensity at the diaphragm. The sound output of thetweeter zone will thereby be maximized for any level of signal currentin such conductors.

It has been discovered that in broad diaphragm areas from which bass andmid-range audio frequency sounds emanate, almost edge areas of thediaphragm have a minimum and alomost negligible vibratory movement orexcursion. principally because the extreme edge is clamped or physicallyretained against movement by the frame. However, such edge areas areextremely important and significant to the transducer because theycontribute materially to the establishment of a desired low resonantfrequency of the diaphragm area of which the edge areas are a part.

Although such edge areas are needed for establishment and maintenanceofdesired resonant frequencies, such edge areas may be simultaneouslyutilized for such strip-like tweeter zones for generating and radiatingthe higher audio frequency sounds. Whereas such edge areas may vibrateslightly with the diaphragm as a whole, such edge areas may beseparately driven or vibrated with higher audio frequency signals togenerate sounds of corresponding frequency.

Such strip-like tweeter zones may transcent diaphragm areas which areotherwise independent of each other. The edge areas of adjacent largeand independent diaphragm areas may be connected together into such aunitary. elongate striplike tweeter zone.

For such a transducer wherein high audio frequency signal carryingconductors are arranged in strip-like tweeter zones along the edge ofthe diaphragm area. and bass and mid-range audio frequency signalcarrying conductors are located predominately in the central or wooferzone ofthc diaphragm area. the magnet or magnetic system producing themagnetic field at the diaphragm may be advantageously arranged. Themagnet may be spaced sufficiently from the woofer zone of the diaphragmarea as to avoid interference with the vibration of the diaphragm.Adjacent the tweeter /one. the magnet may be located extremely close tothe diaphragm.

Other edge areas of the vibrating diaphragm may carry conductors intowhich only mid-range audio frequency signals are supplied. The magnetwill be spaced somewhat farther from such edge areas than from the highfrequency tweeter zones.

Audio frequency signals from the amplifier may be separated forapplication to the energizing conductive means of the diaphragm areas.For instance, in a magnetic transducer (speakers or transducers may alsobe of the electrostatic type) a simple frequency separating network orcrossover circuit may be used. The single output from the amplifier maybe connected directly to the conductors of the tweeter section of thetransducer diaphragm, and the woofer section conductors in series with ablocking coil maybe connected in shunt with the conductors of thetweeter section. The blocking coil will be of such a size as to blockthe high audio frequency signals from the woofer section conductors. Ifseparate mid-range audio frequency signal carrying conductors areutilized on the diaphragm either in a separate zone of the diaphragm orin juxtaposed or clustered relation with the bass signal conductors onthe diaphragm. a separate blocking coil may be seriesconnected with thebass signal conductors to also block the mid-range audio frequencysignals from the bass signal conductors.

Because many. or most. amplifiers currently utilize predominately solidstate components. the use of one or more coils to block high andmid-range audio frequency signals from the bass frequency signalconductors takes advantage of the fact that solid state amplifiers putout their maximum power into low impedance loads. The bass signalconductors. which need the most power to produce bass sounds. presentthe lowest impedance to the amplifier and are therefore supplied with amaximum of power.

The favorable heat dissipation characteristics of the transducer shouldbe noted. The several signal conductors on the diaphragm. in thetweeter. woofer and midrange zones are spread out over a substantialarea. Any heating produced by the substantial current carried by theconductors is rapidly dissipated without any adverse effeet. Heating istherefore not a limiting factor in the amount of power that may besupplied to the transducer. The high energy bass and mid-range frequencysignals need not be blocked from the high frequency tweeter sectionconductors because of the adequate heat dissipation.

One extremely important aspect of this speaker is that the speaker iscomplete with one diaphragm. Sounds across the entire audio frequencyrange are accurately reproduced by the speaker. Because the speaker iscomplete in the use of one diaphragm. numerous and substantial economiesare effected with' out any significant change in sound reproduction.

BRIEF DESCRIPTION OF DRAWINGS FIG. I is a small scale perspective viewillustrating such transducers in use in a room.

FIG. 2 is an elevation view ofthe transducer with the decorative fabriccover removed.

FIG. 3 is an enlarged detail section view taken approximately at 3-3 inFIG. 2.

FIG. 4 is an enlarged detail section view taken approximately at 44 inFIG. 2.

FIG. 5 is a greatly enlarged detail section view taken approximately at5-5 in FIG. 4.

FIG. 6 is a schematic circuit diagram of the transducer for connectionto an amplifier.

FIG. 7 is a slightly modified schematic circuit diagram of thetransducer for connection to the output of an amplifier.

FIG. 8 is an enlarged detail section view somewhat similar to a portionof FIG. 3 and showing a modified form of a portion of the magneticsystem.

FIG. 9 is a detail elevation view illustrating a modified form of theinvention.

FIG. [0 is an enlarged detail section view taken at I0-l0 of FIG. 9 andhaving portions thereof broken away facilitating use of a large scale.

FIG. II is a schematic circuit diagram including the transducer of FIG.9 and adapted for connection to the output of an audio amplifier.

FIG. I2 is an enlarged detail section view showing a modified form ofconductor arrangement on the diaphragm.

FIG. I3 is a diagrammatic section view showing a modified form of theinvention.

FIG. I4 is a view similar to FIG. I3 and showing another modified formof the invention.

FIG. 15 is a view similar to FIG. 13 and showing still another modifiedform of the invention.

DETAILED SPECIFICATION The transducers hereof are indicated in generalby numeral 10 and are generally panel shaped. The transducers are shownin a typical arrangement in FIG. I wherein two such transducers are usedas a part of a stcreophonic system to generate sound in accordance withthe electric signals provided.

These panel shaped transducers may be approximately 5 feet high by 12 toinches wide and approximately an inch in overall thickness. principallydue to the thickness of the frame.

In FIG. I, the transducers are illustrated with plain fabric coverswhich give a desired decorative effect and provide some degree ofprotection for the transducer from physical damage.

The transducer is shown in FIG. 2 and is set into a frame [1.] extendingabout the entire periphery of the transducer to produce a rigidstructure and resist warpage. The frame II.l may be considered a part ofthe rigid backing which is indicated in general by numeral 12 whichprovides the functions of mounting a flexible diaphragm 13 along itsedges and defining fields adjacent the diaphragm. Accordingly. thebacking 12 includes a rigid spacer 11 extending around the entireperiphery of the transducer. and a stiff and generally rigidpanel-shaped armature I4 constructed of magnetic material. specificallya ferrous metal or soft iron material and suitably glavanized to resistcorrosion. Armature 14 is concavely bowed slightly adjacent each dia-Ill phragm area to accommodate diaphragm excursion. The armature panelis affixed adliesively and. in some cases. mechanically. to the spacerII which may be constructed of wood. pressed fiber. rigid plastic.alurninum. iron or other rigid materials. and the panel may beapproximately 18 to 24 gauge galvanized sheet metal. or approximately0.050 inches thickness. The field-generating backing 12 also includes aplurality of elongate thin flexible strips or magnets 15 formed of anysuitable material. but it has been found that a plastic rubber bondedbarium ferrite magnetic material known by its trademark PLASTIFORM soldby Minnesota Mining and Manufacturing Company of St. Paul. Minnesota.has proven satisfactory. It should be recognized that. instead of thestrips. the magnets may be formed in broad sheets of the same material;in any event. the strips or magnets are magnetized in a directiontransversely of the armature plate 14 and of diaphragm I3 so thatelongate magnetic zones are defined which extend all along the length ofthe diaphragm I3. The strips I5 are arranged so that pole faces ofadjoining magnetic zones are of opposite polarity as indicated in FIG.3.

The magnetic fields. in elongate zones. are of maximum strength atlocations just between adjacent strips I5. and. accordingly. theconductors I6 are secured on the diaphragm I3 at locations approximatelybetween adjacent magnetic strips I5.

The backing I2 is acoustically transparent to the sounds produced by thevibrating diaphragm 13, and. accordingly. the plate-like armature 14 hasa plurality of apertures I7 therethrough. The apertures 17 are alignedwith the spaces 18 between the strips or elon gate magnets 15.

The top surfaces or pole faces 19 of the strips or magnets lS are spacedsubstantially from the diaphragm 13 so as to allow the diaphragm to havea significant excursion from its normal position without engaging orimpinging the strips 15.

The diaphragm 13 is divided into a number of substantially independentvibratable areas 130. I3b. l3c. l3d and 13e. each of which is adifferent size than the areas adjacent thereto. Accordingly. each of theseparate vibratable areas I30 I3e has a fundamental resonant frequencywhich is significantly different than the fundamental resonantfrequencies of the other areas. In this version of the transducer. thediaphragm may be uniformly stretched on the spacer ll so that it has apermanent stretch of approximately one percent or more over its naturalsize. Ordinarily. the diaphragm 13 will be stretched in a transversedirection. but may also. if the need arises. be stretched in alongitudinal direction. In order to produce the various fundamentalresonant frequencies at the various areas. the areas may under certaincircumstances all be the same and the mass of the diaphragm in each ofthe areas may be varied slightly so as to produce a differentfundamental resonant frequency.

The areas [3e of the diaphragm are defined by divider strips 20 whichunderlie and are secured as by adhesive to the diaphragm 13. The dividerstrips 20 overlie and bear upon the magnet strips 15. and may beadhesively secured to the magnet strips. The effect of the dividerstrips 20 is to immobilize the diaphragm 13 at each of the strips so asto require that the diaphragm. in each of the vibratable areas 130 l3e.will vibrate independently ofvibrations ofthe diaphragm in each of theother areas.

It will be seen that one end 200 ofeach of the divider strips is locatedin spaced relation with the edge of the diaphragm and the adjacentportions of spacer 11. As a result, there is an elongate narrow strip oredge portion 13.1 of the diaphragm extending longitudinally of thetransducer and along one side of the spacer 11. This elongate edgeportion of the diaphragm is not anchored by the strips and transcendsall of the several vibratable areas 13a l3e. Conducters 16.1 are securedon and extend longitudinally along the full length of the narrow edgeportion 13.] of the diaphragm.

As depicted in FIG. 5. the conductors 16.1, and also conductors 16, aresecured to the diaphragm 13 by an adhesive 21. The backing 12, adjacentthe edge portion 13.1 of the diaphragm includes the elongate stripmagnets 15.1. which are essentially identical to strips 15, but ofsomewhat different dimensions, being somewhat narrower, but somewhatdeeper or thicker. The spacing between the magnet strips 15.1 and theedge portion 13.1ofthc diaphragm is significantly less than the spacingbetween the diaphragm and the strips 15. This smaller spacing adjacentthe edge portion 13.1 of the diaphragm is permissible because the edgeportion of the diaphragm is retained against vibration by the spacer 11and there is no significant excursion of the diaphragm in the edgeportion 13.1.

The divider strips 20 may extend entirely across the diaphragm and tothe opposite spacers 11; however, the strips would have to be thinneradjacent magnets 15.1 to correspond to the reduced spacing between themagnets 15.1 and the diaphragm 13. Such full width strips 20 produce nobearable change as compared to the operation of the constructionillustrated.

Vibration of this portion 13.1 of the diaphragm is caused by vibrationof the adjacent vibratable areas 13a 13e, caused by the application ofan audio frequency signal or current in the conductors 16. Ordinarily,the signal applied to conductors 16 will be of bass audio frequency. ormidrange audio frequency, and, accordingly, the diaphragm areas 130 136*will be vibrated with a corresponding bass audio frequency. Thisvibration of the diaphragm induced by the signal in conductors 16 isproduced in the edge portion 13.1 as well as in the central portions ofthe areas 130 13e. However. because the actual movement of the edgeportion 13.1 of the diaphragm is minimal, there is no significant soundgenerated by the vibration ofthe edge portion 13.1 under influence ofthe bass frequency vibrations. The fact that the edge portion 13.1 is aportion of each of the adjacent vibratable areas 130 13a ofthediaphragm, and is free to vibrate therewith, is extremely significant indefining the fundamental resonant frequency for each particularvibratable area 130 Be. The effective diaphragm area for establishingthe fundamental resonant frequency for any of the particu lar diaphragmareas 130 13s is somewhat larger be cause the edge portion 13.1 isincluded, and therefore the fundamental resonant frequencies of theareas are as low as possible.

The conductors 16.1 which extend along the narrow edge portion 13.1 ofthe diaphragm will ordinarily be high audio frequency signals so as togenerate the corresponding high audio frequency sounds. This edge areaof the transducer including the narrow edge portion 13.1 of thediaphragm is considered a tweeter. As

required to produce a significant sound output from this tweetersection. the pole faces of the magnetic strips 15.1 are located in closeproximity to the diaphragm. The approximate spacing between thediaphragm and the pole faces of the magnetic strips 15.1 may be 0.020inches.

In one example the impedance of the conductors 16 may cumulativelyamount to approximately cumualtive 12 ohms; and, similarly, theconductors 16.1 have cumulative impedance of 12 ohms. A blocking coil 21is connected in series with the conductors 16 to block the high audiofrequency signals from the conductors 16, thus preventing anysignificant generation ofhigh audio frequency sounds thereby, whichsounds would be highly directional. The coil 21 may have an impedance of398 microhenrys. Typically. the conductors 16 are arranged in side byside runs on the diaphragm and are regularly spaced from each other at aspacing of about four conductors per inch. The tweeter conductors 16.1are spaced equally from each other, and approximately eight conductorsper inch. The effective width of the long strip-like tweeter may beapproximately V2 to 1 inch. and the width of the diaphragm area to whichconductors 16 are applied may be approximately seven inches. The rigiddivider strips 20 are approximately 7 inches long. With the transducerconductors connected as indicated in FIG. 6, and connected to the outputof an audio amplifier at the terminals 22. the high audio frequencysignals are effectively blocked from the low audio frequencysignalcarrying conductors 16 on the diaphragm so that the amplifier. ifa solid state amplifier, will put out its maximum power into the lowimpedance load. the conductor 16.

Whereas each of the diaphragm areas 13a 13a includes the adjacent edgeportion 13.1 as a part of it for defining its fundamental resonantfrequency. and driven by bass frequency signals applied in conductors16.1. the edge portion 13.] also acts separately as a tweeter forindependently and separately generating the high range audio frequencysounds.

In another form conductors 16 may be 22 gauge cop per wire in runsapproximately 0.310 in. apart. and conductors 16.1 may be 32 gaugealuminum wire spaced 0.210 in. apart. The mass of the conductors 16.1will be considerably less than the mass of conductors 16. Magnet strips15 may be 0.085 in. thick by 0.260 in. wide and minimally spaced 0.040in. from the half mil diaphragm; and the magnet strips 15.1 may be 0.105in. thick by 0.150 in. wide and spaced 0.020 in. from the diaphragm.Strips 20, with thicknesses of approximately 0.020 to 0.040 in., andspacers 11 maintain the minimum edge spacing in each area 13a 13a, andthe center of each areas has the magnets 15 spaced up to 0.100 inchesfrom the diaphragm by concavely bulging or dishing the metal armatureplate 14 away from the diaphragm.

Published wire conductor data tables indicate that 22 gauge copper wireweights 1.94 pounds per 1,000 feet of wire; and that 32 gauge aluminumwire weighs 0.0589 pounds per 1,000 feet of wire. Simple computationindicates that 22 gauge copper wire therefore weighs 16.2 X 10 poundsper lineal inch; and 32 gauge aluminum weighs 0.491 X 10 pounds perlineal inch. In the foregoing example wherein the 22 gauge copper wiresare in runs approximately 0.310 inches apart, there are approximately3.23 inches of 22 gauge copper conductors 16 per square inch ofdiaphragm area. and therefore the weight of the 22 gauge copperconductor 16 amounts to 52.2 X l()" pounds of copper wire per squareinch of diaphragm area.

The high frequency signal carrying 32 gauge aluminum wire, in theaforesaid example. is in runs 0.210 inches apart. therefore requiring4.76 lineal inches of aluminum wire per square inch of diaphragm areawhich weighs 2.34 X l()' pounds per square inch ofdiaphragm area. Themass or weight of the aluminum wire per square inch of diaphragm areawill therefore be seen to he significantly less than the mass or weightof the 22 gauge copper wire per square inch of diaphragm area. by aratio of approximately I to 22.3. In comparing the relative weights ofthe 32 gauge aluminum and 22 gauge copper wire per square inch ofdiaphragm area. the aluminum wire weighs only 4.5 percent of the weightof the copper wire. or otherwise stated. the mass of the aluminumconductor 16.1 is 95.4 percent less per unit of area of the diaphragmthan the mass of the copper conductor 16.

Low range or bass audio frequency sounds will therefore emanate fromeach of the several vibratable areas 13a l3e in both forward andrearward directions and at all the various angles from side to side. Thehigh range audio frequency sounds are generated at the tweeter strip oredge portion 13.1. and. because of the narrow configuration. these highrange audio frequency sounds will emanate horizontally outwardly insubstantially all directions. both forward and rear.

Although the conductors 16 and 16.] may carry a significant current.there is little concern for heating because the conductors are spreadout widely on the diaphragm with the effect of dispersing large amountsof heat without damage to any of the components.

In the circuit arrangement of FIG. 7. the several conductors 16 and 16.1are typically designed with an impedance of 6 ohms each. The blockingcoil 21 is connected in series with the bass audio frequencysignalreceiving conductor 16, and a condenser 22 of approximatelymicrofarads is connected in series with the tweeter conductor 16.1. Thisarrangement is a conventional L-C crossover circuit. In addition toblocking the high audio frequency signals from the conductor 16, it alsoblocks the low or bass range audio frequency signals from the highfrequency tweeter section or conductors 16.1. The impedance is the sameat any frequency. It can handle larger amplifiers and does not shiftmaximum power to the low frequency end. A more accurate sound is therebyproduced.

The form of the transducer 10.1 illustrated in FIG. 8 is substantiallyidentical to that illustrated in FIGS. 1 5 with the exception that themagnetic strips 15.1 beneath the narrow edge portion or tweeter section13.1 of the transducer are of thin construction and are supported uponan acoustically transparent spacer plate 25 which is a portion of themagnetic armature. The spacer plate 25 is also constructed of a ferrousmetal and preferably a soft iron so as to form a low reluctance path forthe magnetic field, together with the magnet strips 15.1 and thearmature plate 14.

The transducer 10.2 illustrated in FIGS. 9 -11 is substantially the sameas that illustrated in FIGS. 1 S. In this form of transducer, thediaphragm 13 is similarly divided into a number of separate vibratableareas. each with a different fundamental resonant frequency, theseparate vibratable areas illustrated in FIG. 9 being designated 13d and13a. Of course, additional separate vibratahlc areas with differentfundamental resonant frequencies will be utilized as illustrated inconnection with FIG. 2. In this form of the invention. the bass audiofrequency signal-carrying conductors 16 traverse the central portion ofeach of the separate vibratable areas of the diaphragm; and in a mannersimilar to that described in connection with FIGS. 1 5. the high audiofrequency signal-carrying conductor 16.] extends the full length of thenarrow edge portion of tweeter strip 13.1 to generate and emanate highaudio frequency range sounds.

In this form ofthe invention of FIGS. 9 11. an additional edge portion13.2 of the diaphragm remains free of the divider strips 20. both endsof which are in spaced relation with the adjacent frames and the edgesof the diaphragm. However. as in the form of FIGS. 1 5. strips 20 mayextend entirely across the diaphragm to opposite sides of the frame.making provision for varying magnet to diaphragm spacings. The elongateand narrow diaphragm area 13.2 carries additional conductors 16.2 forreceiving midrange audio frequency signals and producing vibration ofthe diaphragm area 13.2 in accordance with these frequencies. As seen inFIG. 11. in addition to the blocking coil 21 which blocks the midrangeand high audio frequency signals from the conductor 16.1. and additionalblocking coil 21.1 is connected in series with the midrange frequencysignal-carrying conductor 16.2 so as to block all of the high rangeaudio frequency signals. Whereas the impedance to high audio frequencysignals remains high at about 12 ohms. the impedance of the transducerto signals in the approximate range of 2 KHz may be approximately 6ohms. while the impedance to signals of approximately 12 Hz may beapproximately 4 ohms. Of course. this provides an advantageous balancingeffect for producing a well balanced sound. Of course, conventional L-Ccrossovers for three way systems may also be used.

Under certain circumstances it may be desirable to produce multiple runsof conductors 16' as illustrated in FIG. 12 over certain of the portionsof the diaphragm for increasing the cooperative effect between thecurrent and the magnetic field for vibrating the conductor and obtainingthe desired excursion.

It will be observed that in FIG. 10, the magnet strips 15.2 adjacent theedge portion 13.2 of the diaphragm are somewhat higher than the strips15 beneath conductors 16 and somewhat lower than the magnet strips 15.1beneath the edge portion 13.1 of the diaphragm. This spacing betweenmagnet strips 15.2 and the diaphragm allows some additional excursion ofthe diaphragm in producing the midrange frequency signals as is requiredfor such signals.

FIGS. 13. 14 and 15 show various modes of producing the variance in thespacing between the diaphragm and the face of the magnet in the backing.In FIG. 13, the armature 14.1, as well as the magnets or strips thereon,are arcuately curved so that the edge portions of the backing includingthe magnet are closer to the diaphragm than the middle portion. In FIG.14. the same armature 14 is utilized as in FIGS. 1 5, but the upperfaces of the magnets or strips 15' on the armature are comulativelyconcavely curved to vary the spacing across the width of the transducer.

The form of the transducer illustrated in FIG. 15 employs acousticallytransparent spacers beneath the magnets at the edge portions of thetransducer. both beneath the tweeter section, but also beneath themidrange audio frequency section of the transducer.

What is claimed is.

l. A sound generating transducer comprising:

a stiff and acoustically transparent backing having a broad andsubstantially flat shape,

an audio sound-producing flexible diaphragm secured to the backing inconfronting relation therewith and defining a vibratable area, the edgesof the vibratable area being stationary against vibration with respectto the backing, the vibratable area of the diaphragm having a centralportion with low frequency signal carrying conductive means thereon forvibrating the entire vibratable area generating low frequency sounds,

said vibratable area also having an elongate and narrow strip portionwith high frequency signal carrying conductive means affixed thereon andsubstantially throughout said strip portion for vibrating the narrowstrip portion of the diaphragm and generating high frequency sounds, andthe mass of the high frequency signal carrying conductor means persquare inch of diaphragm area on said strip portion being substantiallyless than the mass of the low frequency signal carrying conductive meansper sqare inch of area of the diaphragm, and

said backing having means defining polarity characteristics toalternately attract and repel the diaphragm and cause diaphragmvibrations for sound production upon application of audio frequencyelectric signals to the conductive means.

2. The transducer according to claim 1 and the backing being spacedsignificantly closer to the diaphragm at said narrow strip portions thanat said central portion of the vibratable area.

3. The transducer according to claim I and both of the conductive meansincluding current carrying conduetors on the diaphragm, the highfrequency signal conductors on the narrow strip portion havingsignificantly less mass per unit of lenth than the low frequencyconductors on the central portion of the vibratable area, and thepolarity characteristics defining means of the backing being magnetic.

4. A sound generating transducer comprising:

a stiff and acoustically transparent backing having a broad andsubstantially flat shape,

an audio sound-producing flexible diaphragm having its edges secured tothe backing, the diaphragm being disposed in confronting and spacedrelation with the backing and having a pair of adjacent vibratableareas, each of said vibratable areas having a central portion withconductive means thereon to receive bass audio frequency signals forvibrating the diaphragm area as a woofer,

divider means between said adjacent vibratable areas and engaging andretaining the diaphragm against vibrating at the edge of the vibratableareas,

the diaphragm having an elongate and narrow edge portion extending intoboth vibratable areas, said elongate and narrow edge portion of thediaphragm having conductive means thereon to receive high audiofrequency signals for vibrating the narrow edge portion of the diaphragmas a tweeter, the tweeter forming a portion of and transcending adjacentwoofers, and

said backing having means defining polarity characteristics toalternatively attract and repel the diaphragm and cause diaphragmvibrations for sound production upon application of audio frequencyelectric signals to the conductive means.

5. The sound generating transducer according to claim 4 and said pair ofadjacent vibratable areas ofthe diaphragm having different fundamentalresonant frequencies separated significantly from each other.

6. The sound generating transducer according to claim 4 wherein bothends of the divider means are re spectively spaced from opposite edgesof the diaphragm, and

the diaphragm also having an elongate edge portion located along theedge of the diaphragm opposite the tweeter and also extending across theadjoining end of the divider means and into both vibratable areas andcarrying conductive means to receive midrange audio frequency signalsfor vibrating the diaphragm.

7. The sound generating transducer according to claim 4 and the dividermeans having one end in spaced relation with one edge of the diaphragm,said one end being disposed adjacent the tweeter.

8. The sound generating transducer according to claim 4 and saidacoustically transparent backing including a magnetic means.

the woofer and tweeter conductive means including current-carryingconductors cooperating with the magnetic means ofthc backing invibrating the diaphram.

9. The sound generating transducer according to claim 8 and theconductors of the tweeter extending the full length of the tweeter andinto both adjacent vibrating areas of the diaphragm,

10. The sound generating transducer according to claim 9 and theconductors of the tweeter extending longitudinally of the tweeterthroughout substantially the full length of the diaphragm and to theedges thereof.

11. A sound generating transducer comprising:

a stiff and acoustically transparent backing having a broad andsubstantially flat shape and including a magnetic means producingmagnetic fields adjacent the backing,

an audio sound-producing flexible diaphragm sccured to the backing inconfronting relation therewith and defining a vibratable area, the edgesof the vibratable are being stationary against vibration with respect tothe backing, the vibratable area of the diaphragm having a centralportion with current-carrying conductors thereon to receive low audiofrequency signals for vibrating the entire vibratable area,

said vibratable area also having an elongate and narrow edge portionwith current-carrying conductors thereon to receive high audio frequencysignals for vibrating the narrow edge portion of the diaphragm, and themagnetic means of said backing having pole faces confronting thediaphragm and lying parallel to the diaphragm adjacent said elongatenarrow edge portion and the pole faces also being spaced significantlycloser to the diaphragm adjacent said elongate narrow edge portion thanat said central portion.

12. The sound generating transducer according to claim 11, and saidmagnetic means including a platelike armature of magnetic material, andfield generating means on the armature adjacent the central and alongthe narrow edge portions of the vibratable area.

[3. The sound generating transducer according to claim I2 and the fieldgenerating means including thin flexible magnets magnetically adhered tothe armature and variously spaced from the diaphragm adjacent the edgeportion and central portion of the vibratable area,

[4. The sound generating transducer according to claim I], and theconductors of the central and edge portions being separated from eachother without overlap or commingling IS. The sound generating transduceraccording to claim 11 and including a blocking coil connected in serieswith the current-carrying conductors on the central portion to excludethe high audio frequency signals therefrom,

[6. A sound generating transducer comprising:

a stiff and acoustically transparent hacking having a broad andsubstantially flat shape. the hacking ineluding magnetic means definingelongate zones to form magnetic pole faces. adjacent pole faces being ofopposite polarity to define a plurality of elongate magnetic fieldsadjoining the magnetic means.

an audio sound-producing flexible diaphragm having edges secured to thebacking in confronting and spaced relation therewith and defining avibratable area. the edges of the vibratable area being stationaryagainst vibration with respect to the backing. the vibratable area ofthe diaphragm having a central portion with current-carrying conductorsthereon and extending along the elongate zones of the magnetic means toreceive low audio frequency signals and causing vibration of the entirevibratable area and generating low frequency sounds.

said vibratable area also having an elongate and narrow edge portionwith current-carrying conductors thereon and extending along theelongate zones of the magnetic means to receive high audio frequencysignals for vibrating the narrow edge portion of the diaphragm, and

the conductors in the elongate and narrow edge portion having a spacingfrom each other significantly less than the spacing between adjacentconductors at the central portion of the vibratable area. and theelongatc zones and magnetic pole faces of the magnetic means beingspaced from adjacent zones and faces in accordance with the spacingbetween adjacent conductors on the diaphragm.

17. The sound generating transducer according to claim l6, and the polefaces of the magnetic means being uniformly spaced from the diaphragmadjacent the elongate narrow edge portion of the vibratable area. andalso being positioned significantly closer to the diaphragm andconductors thereon adjacent the elongate narrow edge portion of saidarea than adja cent the conductors on the central portion of the vihratable area.

18. The sound generating transducer according tr claim 16 and the fieldgenerating means having a generally concavely shaped surface confrontingand facing the diaphragm and being spaced significantly closer tr theelongate and narrow edge portion of the vibratable area than from thecentral portion of the vibratablc area of the diaphragm;

19. A sound generating transducer comprising:

a stiff and acoustically transparent backing having a broad andsubstantially flat shape. the backing including magnetic means defininga plurality of elongate and parallel magnetic zones forming magneticpole faces. adjacent pole faces being ofopposite polarity to define aplurality of elongate magnetic fields adjoining such faces an audiosound producing flexible diaphragm having edges secured to the backingand defining a vibratable area in confronting and spaced relation withsaid pole faces. the diaphragm being permanently stretched in excess ofits natural size, but within the elastic limits of the diaphragm.

the vibratable area ofthe diaphragm having adjoining portions withcurrent carrying conductors thereon and extending along the elongatezones ofthe magnetic means. one of said portions of the vibratable areabeing broad with low frequency carrying conductors thereon and extendingalong the elongate zones of the magnetic means to receive low audiofrequency signals and causing vibration of the entire vibratable areaand generating sounds of comparable low frequencies,

another of said portions of the vibratable area being in the form of anelongate and narrow strip with high frequency conductors thereon andextending along the elongate zones of the magnetic means to receive highaudio frequency signals for vibrating the elongate and narrow strip atsuch high audio frequencies. the spacing between said high frequencycurrent carrying conductors in said strip being significantly less thanthe spacing between the low frequency carrying conductors on thediaphragm, the width of said elongate magnetic zones adjacent said highfrequency current carrying conductors being substantially less than thewidth of the elongate magnetic zones adjacent said low frequencycarrying conductors and the spacing between adjacent elongate mangeticzones conforming to the corresponding spacing between the adjacent lowfrequency and high frequency current carrying conductors on thediaphragm, respectively,

1. A sound generating transducer comprising: a stiff and acousticallytransparent backing having a broad and substantially flat shape, anaudio sound-producing flexible diaphragm secured to the backing inconfronting relation therewith and defining a vibratable area, the edgesof the vibratable area being stationary against vibration with respectto the backing, the vibratable area of the diaphragm having a centralportion with low frequency signal carrying conductive means thereon forvibrating the entire vibratable area generating low frequency sounds,said vibratable area also having an elongate and narrow strip portionwith high frequency signal carrying conductive means affixed thereon andsubstantially throughout said strip portion for vibrating the narrowstrip portion of the diaphragm and generating high frequency sounds, andthe mass of the high frequency signal carrying conductor means persquare inch of diaphragm area on said strip portion being substantiallyless than the mass of the low frequency signal carrying conductive meansper sqare inch of area of the diaphragm, and said backing having meansdefining polarity characteristics to alternately attract and repel thediaphragm and cause diaphragm vibrations for sound production uponapplication of audio frequency electric signals to the conductive means.2. The transducer according to claim 1 and the backing being spacedsignificantly closer to the diaphragm at said narrow strip portions thanat said central portion of the vibratable area.
 3. The transduceraccording to claim 1 and both of the conductive means including currentcarrying conductors on the diaphragm, the high frequency signalconductors on the narrow strip portion having significantly less massper unit of lenth than the low frequency conductors on the centralportion of the vibratable area, and the polarity characteristicsdefining means of the backing being magnetic.
 4. A sound generatingtransducer comprising: a stiff and acoustically transparent backinghaving a broad and substantially flat shape, an audio sound-producingflexible diaphragm having its edges secUred to the backing, thediaphragm being disposed in confronting and spaced relation with thebacking and having a pair of adjacent vibratable areas, each of saidvibratable areas having a central portion with conductive means thereonto receive bass audio frequency signals for vibrating the diaphragm areaas a woofer, divider means between said adjacent vibratable areas andengaging and retaining the diaphragm against vibrating at the edge ofthe vibratable areas, the diaphragm having an elongate and narrow edgeportion extending into both vibratable areas, said elongate and narrowedge portion of the diaphragm having conductive means thereon to receivehigh audio frequency signals for vibrating the narrow edge portion ofthe diaphragm as a tweeter, the tweeter forming a portion of andtranscending adjacent woofers, and said backing having means definingpolarity characteristics to alternatively attract and repel thediaphragm and cause diaphragm vibrations for sound production uponapplication of audio frequency electric signals to the conductive means.5. The sound generating transducer according to claim 4 and said pair ofadjacent vibratable areas of the diaphragm having different fundamentalresonant frequencies separated significantly from each other.
 6. Thesound generating transducer according to claim 4 wherein both ends ofthe divider means are respectively spaced from opposite edges of thediaphragm, and the diaphragm also having an elongate edge portionlocated along the edge of the diaphragm opposite the tweeter and alsoextending across the adjoining end of the divider means and into bothvibratable areas and carrying conductive means to receive midrange audiofrequency signals for vibrating the diaphragm.
 7. The sound generatingtransducer according to claim 4 and the divider means having one end inspaced relation with one edge of the diaphragm, said one end beingdisposed adjacent the tweeter.
 8. The sound generating transduceraccording to claim 4 and said acoustically transparent backing includinga magnetic means, the woofer and tweeter conductive means includingcurrent-carrying conductors cooperating with the magnetic means of thebacking in vibrating the diaphram.
 9. The sound generating transduceraccording to claim 8 and the conductors of the tweeter extending thefull length of the tweeter and into both adjacent vibrating areas of thediaphragm.
 10. The sound generating transducer according to claim 9 andthe conductors of the tweeter extending longitudinally of the tweeterthroughout substantially the full length of the diaphragm and to theedges thereof.
 11. A sound generating transducer comprising: a stiff andacoustically transparent backing having a broad and substantially flatshape and including a magnetic means producing magnetic fields adjacentthe backing, an audio sound-producing flexible diaphragm secured to thebacking in confronting relation therewith and defining a vibratablearea, the edges of the vibratable are being stationary against vibrationwith respect to the backing, the vibratable area of the diaphragm havinga central portion with current-carrying conductors thereon to receivelow audio frequency signals for vibrating the entire vibratable area,said vibratable area also having an elongate and narrow edge portionwith current-carrying conductors thereon to receive high audio frequencysignals for vibrating the narrow edge portion of the diaphragm, and themagnetic means of said backing having pole faces confronting thediaphragm and lying parallel to the diaphragm adjacent said elongatenarrow edge portion and the pole faces also being spaced significantlycloser to the diaphragm adjacent said elongate narrow edge portion thanat said central portion.
 12. The sound generating transducer accordingto claim 11, and said magnetic means including a plate-like armature ofmagnetic material, and field generating means on the armature adjacentthe central and Along the narrow edge portions of the vibratable area.13. The sound generating transducer according to claim 12 and the fieldgenerating means including thin flexible magnets magnetically adhered tothe armature and variously spaced from the diaphragm adjacent the edgeportion and central portion of the vibratable area.
 14. The soundgenerating transducer according to claim 11, and the conductors of thecentral and edge portions being separated from each other withoutoverlap or commingling.
 15. The sound generating transducer according toclaim 11 and including a blocking coil connected in series with thecurrent-carrying conductors on the central portion to exclude the highaudio frequency signals therefrom.
 16. A sound generating transducercomprising: a stiff and acoustically transparent backing having a broadand substantially flat shape, the backing including magnetic meansdefining elongate zones to form magnetic pole faces, adjacent pole facesbeing of opposite polarity to define a plurality of elongate magneticfields adjoining the magnetic means, an audio sound-producing flexiblediaphragm having edges secured to the backing in confronting and spacedrelation therewith and defining a vibratable area, the edges of thevibratable area being stationary against vibration with respect to thebacking, the vibratable area of the diaphragm having a central portionwith current-carrying conductors thereon and extending along theelongate zones of the magnetic means to receive low audio frequencysignals and causing vibration of the entire vibratable area andgenerating low frequency sounds, said vibratable area also having anelongate and narrow edge portion with current-carrying conductorsthereon and extending along the elongate zones of the magnetic means toreceive high audio frequency signals for vibrating the narrow edgeportion of the diaphragm, and the conductors in the elongate and narrowedge portion having a spacing from each other significantly less thanthe spacing between adjacent conductors at the central portion of thevibratable area, and the elongate zones and magnetic pole faces of themagnetic means being spaced from adjacent zones and faces in accordancewith the spacing between adjacent conductors on the diaphragm.
 17. Thesound generating transducer according to claim 16, and the pole faces ofthe magnetic means being uniformly spaced from the diaphragm adjacentthe elongate narrow edge portion of the vibratable area, and also beingpositioned significantly closer to the diaphragm and conductors thereonadjacent the elongate narrow edge portion of said area than adjacent theconductors on the central portion of the vibratable area.
 18. The soundgenerating transducer according to claim 16 and the field generatingmeans having a generally concavely shaped surface confronting and facingthe diaphragm and being spaced significantly closer to the elongate andnarrow edge portion of the vibratable area than from the central portionof the vibratable area of the diaphragm.
 19. A sound generatingtransducer comprising: a stiff and acoustically transparent backinghaving a broad and substantially flat shape, the backing includingmagnetic means defining a plurality of elongate and parallel magneticzones forming magnetic pole faces, adjacent pole faces being of oppositepolarity to define a plurality of elongate magnetic fields adjoiningsuch faces, an audio sound producing flexible diaphragm having edgessecured to the backing and defining a vibratable area in confronting andspaced relation with said pole faces, the diaphragm being permanentlystretched in excess of its natural size, but within the elastic limitsof the diaphragm, the vibratable area of the diaphragm having adjoiningportions with current carrying conductors thereon and extending alongthe elongate zones of the magnetic means, one of said portions of thevibratable area being broad with low frequency carrying conductorsthereon and extending along the elongate zones of the magnetic means toreceive low audio frequency signals and causing vibration of the entirevibratable area and generating sounds of comparable low frequencies,another of said portions of the vibratable area being in the form of anelongate and narrow strip with high frequency conductors thereon andextending along the elongate zones of the magnetic means to receive highaudio frequency signals for vibrating the elongate and narrow strip atsuch high audio frequencies, the spacing between said high frequencycurrent carrying conductors in said strip being significantly less thanthe spacing between the low frequency carrying conductors on thediaphragm, the width of said elongate magnetic zones adjacent said highfrequency current carrying conductors being substantially less than thewidth of the elongate magnetic zones adjacent said low frequencycarrying conductors, and the spacing between adjacent elongate mangeticzones conforming to the corresponding spacing between the adjacent lowfrequency and high frequency current carrying conductors on thediaphragm, respectively.